Colinearity depends on which chromosome is the standard and which is the tester. Each row shows the centimorgan location of a hypothetical marker that cross-hybridizes to two chromosomes. (Gray arrows) Colinear runs of markers between the chromosomes. (A) With chromosome I as the standard, a colinear run contains six markers. (B) With chromosome II as the standard, the longest run has four markers. Such asymmetry is common in maize data and probably represents intrachromosomal rearrangements.